1. Field of the Invention
The present invention relates to a creasing device for a corrugated board sheet and a corrugated-box making machine for making a corrugated box using the corrugated board sheet.
2. Description of the Related Art
A corrugated-box making machine generally makes a corrugated box from a corrugated board sheet having a fluted inner sheet glued between linerboards. The corrugated-box making machine generally includes a feeding unit, a printing unit, a slotter-creaser unit, a folding unit, and a counter-ejector unit.
The feeding unit includes a kicker and a pair of feed rolls to feed a corrugated board sheet to a printing unit. Specifically, the kicker is reciprocated by a crank lever to kick out a corrugated board sheet piled on a table, and the feed rolls nip the corrugated board sheet to convey it to the printing unit at a predetermined speed.
The printing unit performs a monochrome or a multicolor printing, and includes at least one printing unit. The printing unit includes a printing cylinder with a printing die. An ink supply roll is arranged near the printing cylinder and in contact with the printing die. An ink chamber, in which ink is contained, is arranged near the ink supply roll. Upon printing an image or a text, the ink chamber supplies the ink onto a surface of the ink supply roll, and the applied ink is transferred onto the printing die. A counter roll is arranged below the printing cylinder so that the corrugated board sheet is nipped between the printing die and the counter roller for the printing.
The slotter-creaser unit performs a creasing process by a first creasing roll and a second creasing roll on a printed corrugated board sheet, and then performs a slotting process by a slotter knife on a creased corrugated board sheet.
The folding unit conveys the corrugated board sheet to a glue applying unit to apply glue onto a joint flap. The corrugated board sheet with the glue applied is further conveyed to the folding bar and a folding belt to fold the corrugated board sheet thereby jointing the joint flap. As a result, a corrugated box is formed. The counter-ejector unit piles the corrugated box formed by folding and gluing the corrugated board sheet in a hopper unit. A predetermined number of piled corrugated boxes are grouped into a batch, and the batch is delivered.
The slotter-creaser unit in the above corrugated-box making machine is configured to form a crease necessary for folding the corrugated board sheet by the folding unit. The slotter-creaser unit includes a rotatable creasing roll and a counter roll arranged opposite to the creasing roll. The creasing roll is fixed to a crease shaft, and a protruding portion corresponding to a center portion of the crease is arranged on the periphery of the creasing roll in the circumferential direction. Furthermore, pressing portions are arranged on the both sides of the protruding portion in the circumferential direction. When the corrugated board sheet is nipped between the creasing roll and the counter roll while being conveyed, the protruding portion of the creasing roll forms a crease along with a flute of the fluted inner sheet and the pressing portion forms a pressed portion on the both sides of the crease. Therefore, the corrugated board sheet can be folded along the crease with the pressed portion by the folding unit.
The above creasing devices are disclosed in, for example, Japanese Patent Application Laid-open No. 2001-328181 and Japanese Patent Application Laid-open No. 2005-035076.
A configuration of the fluted inner sheet glued between an outer linerboard and an inner linerboard of the corrugated board sheet can be changed depending on its use. Specifically, the strength of the corrugated board sheet can be changed depending on various factors. Examples of the factors include a height and a pitch of a flute of the fluted inner sheet, a thickness and sheet quality of the inner linerboard, the outer linerboard, and the fluted inner sheet, and the number of the fluted inner sheets to be sandwiched between the outer and the inner linerboards.
To manufacture the corrugated box with desired quality by the corrugated-box making machine, it is necessary to fold the corrugated board sheet appropriately at a predetermined position. Therefore, a crease needs to be formed clearly at an accurate position. The slotter-creaser unit in the conventional corrugated-box making machine can set a width of the pressing portion of the creasing roll depending on the strength of the corrugated board sheet. Specifically, when the strength of the corrugated board sheet is high, the width of the pressing portion is set wide to form a wide pressed portion on the both sides of the crease. Therefore, portions (inner parts) on the both sides of the crease do not interfere with each other when the corrugated board sheet is folded. Thus, degree of folding precision can be preserved. On the other hand, when the strength of the corrugated board sheet is low, the width of the pressing portion is set narrow to form a narrow pressed portion on the both sides of the crease. Therefore, a folding position can be uniformly set to assuredly fold the corrugated board sheet at the crease position to prevent degradation of the folding precision.
However, if the creasing roll is replaced depending on the strength of the corrugated board sheet to be processed into the corrugated box, it is necessary to suspend the corrugated-box making machine during a processing operation, resulting in degradation of operation efficiency. Therefore, the conventional corrugated-box making machine generally sets a width of the pressing portion to a normal width applicable for the corrugated board sheets with both high strength and low strength to eliminate necessity of replacement of the creasing roll. As a result, the pressed portion is not wide enough for the corrugated board sheet with high strength while it is too narrow for the corrugated board sheet with low strength. Thus, the folding position cannot be set uniform, resulting in degradation of the folding precision.